Incorporated herein by reference is the disclosure of copending U.S. patent application Ser. No. 08/115,810, filed Sep. 3, 1993, and entitled "Video Merging Employing Pattern-key Insertion", now abandoned, which is assigned to the same assignee as the present application. As taught in that patent application, pattern-key insertion is used to derive a composite image by merging foreground and background implementation techniques used for this purpose is one in which an estimate of the location of a target region can be inferred from the tracked location of any of multiple landmark regions in the background image. The location of each of the multiple landmark regions may be displaced in a different direction from the location of the target region, so that in case the video scene is such that the target region itself moves partially or completely beyond a particular edge of the image, at least one of the tracked multiple landmark regions remains within the image so that even if the location of the target region itself is partially or wholly outside of the image field of view, inferred tracking of the target region itself can still be continuously maintained. In addition, Any of the tracked multiple landmark regions in the image may be occluded at times by the presence of a foreground object in the scene, so it cannot be used at such times for inferring the the location of the target region. In such a case, another of the tracked multiple landmark regions in the image must be used instead. However, it has been found that switching from one tracked multiple landmark region to another tracked multiple landmark region for use in inferring the location of the target pattern results in model errors that cause unstable estimates of the location of the target pattern
Such model errors could be reduced by fitting higher order models to the respective tracked multiple landmark regions so that they are tracked better. Such higher order models are unstable to estimate from a single image frame, and biased errors in local estimates introduce estimation errors that are difficult to model a priori.
The present invention is directed to an improved technique for deriving stable estimates of the location of the target pattern when one tracked multiple landmark region is switched to another tracked multiple landmark region for use in inferring the location of a target pattern.